Fabrication of vertical field effect transistors with uniform structural profiles

ABSTRACT

Semiconductor devices are fabricated with vertical field effect transistor (FET) devices having uniform structural profiles. Semiconductor fabrication methods for vertical FET devices implement a process flow to fabricate dummy fins within isolation regions to enable the formation of vertical FET devices with uniform structural profiles within device regions. Sacrificial semiconductor fins are formed in the isolation regions concurrently with semiconductor fins in the device regions, to minimize/eliminate micro-loading effects from an etch process used for fin patterning and, thereby, form uniform profile semiconductor fins. The sacrificial semiconductor fins within the isolation regions also serve to minimize/eliminate non-uniform topography and micro-loading effects when planarizing and recessing conductive gate layers and, thereby. form conductive gate structures for vertical FET devices with uniform gate lengths in the device regions. The sacrificial semiconductor fins are subsequently removed and replaced with insulating material to form the dummy fins.

TECHNICAL FIELD

This disclosure relates generally to semiconductor fabricationtechniques and, in particular, to structures and methods for fabricatingvertical field effect transistor (FET) devices.

BACKGROUND

Traditional CMOS (complementary metal oxide semiconductor) techniquesinclude process flows for constructing planar FET devices. With planarFETs, increased transistor density can be achieved by decreasing thepitch between transistor gate elements. However, with planar FETdevices, the ability to decrease gate pitch is limited by the requiredgate length and spacer thickness. In recent years, there has beensignificant research and development with regard to vertical FETdevices, which decouple the gate length from the gate pitch requirementand enable scaling of transistor density. In general, vertical FETdevices are designed to have gate structures that are formed on multiplesides of a vertical channel structure (e.g., a vertical semiconductorfin or vertical nanowire). In addition, vertical FET devices employdoped source and drain regions, wherein a doped source region for avertical FET can be formed on top of a vertical semiconductor fin, andwherein a doped drain region can be formed underneath the verticalsemiconductor fin. With vertical FET devices, scaling is determined byhow close vertical conductive contacts to the source and drain regionscan be placed.

In semiconductor devices where different pattern densities of devicestructures are formed on a semiconductor substrate, the ability tofabricate device structures with uniform structural profiles within thesame device region or adjacent device regions is problematic andchallenging because of the micro-loading effects of conventional etchand planarizing processes. For example, with vertical FET devices, agate length of a metal gate is defined by a timed etching of a layer ofconductive gate material, typically performed by a reactive ion etch(RIE). Due to the micro-loading effects of the RIE process, there can bea relatively large variation in the gate length of vertical FET devicesbetween dense vertical FET regions and isolated vertical FET regions.Indeed, the metal gate recess level in a given region is dependent, forexample, on the pattern density of vertical semiconductor fins (e.g.,pitch) within the given region, where the conductive gate layer may berecessed deeper in regions of the semiconductor substrate havingrelaxed-pitch vertical semiconductor fin patterns as compared to regionsof the semiconductor substrate having tight-pitch vertical semiconductorfin patterns. Even within the same device region, gate length variationcan occur between vertical FET devices formed within a center region ofa given device region and vertical FET devices formed at the edges ofthe given device region.

Another issue with conventional vertical FET device fabrication is theinitial variation in thickness of a planarized layer of conductive gatematerial (prior to the gate recess), which results from dishing effectsthat can result from chemical mechanical polishing (CMP). Themicro-loading effects of conventional etch and planarizing processesduring vertical FET device fabrication can result in undesired variationin device dimensions, which leads to undesired variation in deviceperformance.

SUMMARY

Embodiments of the invention include methods for fabricating verticalFET devices with uniform structural profiles, as well as semiconductordevices comprising vertical FET devices with uniform structure profiles.

For example, one embodiment of the invention includes a method forfabricating a semiconductor device. The method comprises forming asubstrate comprising a lower source/drain layer disposed between a basesemiconductor substrate and a first layer of semiconductor material. Ashallow trench isolation (STI) layer is formed through a portion of thefirst layer of semiconductor material, the lower source/drain layer andinto an upper portion of the semiconductor substrate to form anisolation region, wherein the isolation region defines a first deviceregion comprising a first lower source/drain region and a second deviceregion comprising a second lower source/drain region. The STI layer isrecessed, and a second layer of semiconductor material is formed on therecessed STI layer in the isolation region. The first and second layersof semiconductor material are concurrently patterned using a first etchprocess to form an array of vertical semiconductor fins in the first andsecond device regions and the isolation region. A lower insulatingspacer is formed on the first and second lower source/drain regions andthe STI layer. A conductive gate structure is formed on the lowerinsulating spacer and surrounding sidewalls of the verticalsemiconductor fins in the first and second device regions and theisolation region. An upper insulating spacer is formed on the conductivegate structure. The vertical semiconductor fins in the isolation regionare then etched away using a second etch process which is selective tothe vertical semiconductor fins in the first and second device regions,to form trenches down to the STI layer in the isolation region. Thetrenches in the isolation region are filled with an insulating materialto form vertical dummy fins in the isolation region.

Another embodiment includes a semiconductor device. The semiconductordevice comprises: a first vertical FET device formed in a first deviceregion of a substrate, wherein the first vertical FET device comprisesvertical semiconductor fins; a second vertical FET device formed in asecond device region of the substrate, wherein the second vertical FETdevice comprises vertical semiconductor fins; an isolation regionseparating the first and second device regions, wherein the isolationregion comprises a STI layer formed in the substrate, and a plurality ofvertical dummy fins disposed on the STI layer in the isolation region;and a conductive gate structure disposed around sidewalls of thevertical semiconductor fins of the first and second FET devices in thefirst and second device regions and around sidewalls of the verticaldummy fins in the isolation region.

Other embodiments will be described in the following detaileddescription of embodiments, which is to be read in conjunction with theaccompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional side view of a semiconductordevice comprising vertical FET devices, according to an embodiment ofthe invention.

FIGS. 2 through 17 schematically illustrate a method for fabricating thesemiconductor device of FIG. 1 according to an embodiment of theinvention, wherein:

FIG. 2 is a schematic cross-sectional side view of the semiconductordevice at an intermediate stage of fabrication in which a lowersource/drain layer and a monocrystalline semiconductor layer are formedon a semiconductor substrate;

FIG. 3 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 2 after forming a STI layer that defines an isolationregion and separate active device regions;

FIG. 4 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 3 after recessing the STI layer down to a lower regionof the monocrystalline semiconductor layer;

FIG. 5 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 4 after forming a sacrificial semiconductor layer onthe recessed STI layer;

FIG. 6 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 5 after forming a hardmask layer on the surface of thesemiconductor structure;

FIG. 7 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 6 after patterning the hardmask layer to form an etchhardmask, and patterning the monocrystalline semiconductor layer and thesacrificial semiconductor layer using the image of the etch hardmask toform an array of vertical semiconductor fins in the isolation and activedevice regions;

FIG. 8 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 7 after forming a lower insulating spacer and aconformal layer of gate dielectric material;

FIG. 9 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 8 after depositing and planarizing a layer ofconductive material that is used to form a gate electrode layer;

FIG. 10 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 9 after recessing the layer of conductive material toform a gate electrode layer with a thickness that defines a gate lengthof vertical FET devices to be formed in the active device regions;

FIG. 11 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 10 after removing exposed portions of the gatedielectric layer on upper portions of the vertical fins in the activedevice and isolation regions to form a conductive gate structure;

FIG. 12 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 11 after forming an upper insulating spacer on anupper surface of the conductive gate structure;

FIG. 13 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 12 after depositing a layer of insulating material onthe surface of the semiconductor structure and planarizing the surfacedown to expose the etch hardmask on top of the vertical fins in theactive device and isolation regions;

FIG. 14 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 13 after removing the etch hardmask to expose uppersurfaces of the vertical fins in the active device and isolationregions;

FIG. 15 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 14 after removing sacrificial vertical semiconductorfins in the isolation region to form trenches down to the STI layer;

FIG. 16 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 15 after filling the trenches with an insulatingmaterial to form vertical dummy fins in the isolation region;

FIG. 17 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 16 after recessing the insulating material down to alevel which exposes upper surfaces of the vertical semiconductor fins inthe active device regions and which recesses upper surfaces of thevertical dummy fins in the isolation region to be substantially levelwith the upper surfaces of the vertical semiconductor fins in the activedevice regions; and

FIG. 18 is a schematic cross-sectional side view of the semiconductorstructure of FIG. 17 after removing the layer of insulating material onthe upper insulating spacer, and epitaxially growing upper source/drainregions on the exposed upper portions of the vertical semiconductor finsin the active device regions.

DETAILED DESCRIPTION

Embodiments of the invention will now be described with regard methodsfor fabricating vertical FET devices with uniform structural profiles,as well as semiconductor devices comprising vertical FET devices withuniform structural profiles. Semiconductor fabrication methods forvertical FET devices according to embodiments of the invention implementa process flow to fabricate vertical dummy fins within isolationregions, which enables the formation of vertical FET devices withuniform structural profiles within device regions. For example, asexplained in further detail below, a fin patterning process isimplemented to form sacrificial vertical semiconductor fins in theisolation regions concurrently with vertical semiconductor fins in thedevice regions. The concurrent formation of the vertical semiconductorfins in the device and isolation regions serves to minimize/eliminatemicro-loading effects of an etch process that is utilized for the finpatterning process, thereby resulting in the formation of uniformvertical semiconductor fins in the device regions. The sacrificialvertical semiconductor fins within the isolation regions also serve tominimize/eliminate non-uniform topography and micro-loading effects whenchemical-mechanical planarizing and recessing conductive gate layers,thereby resulting in the formation of conductive gate structures for thevertical FET devices with uniform gate lengths in the device regions.The sacrificial vertical semiconductor fins in the isolation regions aresubsequently removed and replaced with insulating material to form thevertical dummy fins.

It is to be understood that the various layers, structures, and regionsshown in the accompanying drawings are schematic illustrations that arenot drawn to scale. In addition, for ease of explanation, one or morelayers, structures, and regions of a type commonly used to formsemiconductor devices or structures may not be explicitly shown in agiven drawing. This does not imply that any layers, structures, andregions not explicitly shown are omitted from the actual semiconductorstructures. Furthermore, it is to be understood that the embodimentsdiscussed herein are not limited to the particular materials, features,and processing steps shown and described herein. In particular, withrespect to semiconductor processing steps, it is to be emphasized thatthe descriptions provided herein are not intended to encompass all ofthe processing steps that may be required to form a functionalsemiconductor integrated circuit device. Rather, certain processingsteps that are commonly used in forming semiconductor devices, such as,for example, wet cleaning and annealing steps, are purposefully notdescribed herein for economy of description.

Moreover, the same or similar reference numbers are used throughout thedrawings to denote the same or similar features, elements, orstructures, and thus, a detailed explanation of the same or similarfeatures, elements, or structures will not be repeated for each of thedrawings. It is to be understood that the terms “about” or“substantially” as used herein with regard to thicknesses, widths,percentages, ranges, etc., are meant to denote being close orapproximate to, but not exactly. For example, the term “about” or“substantially” as used herein implies that a small margin of error ispresent, such as 1% or less than the stated amount. Further, the term“vertical” or “vertical direction” or “vertical height” as used hereindenotes a Z-direction of the Cartesian coordinates shown in thedrawings, and the terms “horizontal,” or “horizontal direction,” or“lateral direction” as used herein denotes an X-direction and/orY-direction of the Cartesian coordinates shown in the drawings.

FIG. 1 is a schematic cross-sectional side view of a semiconductordevice 100 comprising vertical FET devices, according to an embodimentof the invention. The semiconductor device 100 comprises a basesemiconductor substrate 102, lower source/drain regions 104-1 and 104-2,a STI layer 110, a plurality of vertical semiconductor fins 121, 122,123, 127, 128, and 129, a plurality of vertical dummy fins 124′, 125′,and 126′, a lower insulating spacer 130, a conductive gate structure155, an upper insulating spacer 160, upper source/drain regions 170-1and 170-2, an insulating layer 180, and vertical source/drain contacts190-1 and 190-1. The conductive gate structure 155 comprises a thin gatedielectric layer 140 disposed on sidewalls of the vertical semiconductorfins 121, 122, 123, 127, 128, and 129 and the vertical dummy fins 124′,125′, and 126′, and a gate electrode layer 150 comprising a layer ofconductive material disposed around and between the verticalsemiconductor fins 121, 122, 123, 127, 128, and 129 and the verticaldummy fins 124′, 125′, and 126′. It is to be understood that the term“source/drain region” as used herein means that a given source/drainregion can be either a source region or a drain region, depending on theapplication or circuit configuration.

The example embodiment of FIG. 1 shows a plurality of different regionsincluding, for example, first and second device regions R1 and R2, andan isolation region R3 defined by the STI layer 110. The first deviceregion R1 comprises at least one vertical FET device which comprisesthree vertical semiconductor fins 121, 122 and 123 commonly connected atone end to the lower source/drain region 104-1 and having separate uppersource/drain regions 170-1 epitaxially grown on opposing ends ofvertical semiconductor fins 121, 122 and 123. The vertical source/draincontact 190-1 is commonly connected to each of the upper source/drainregions 170-1. In this configuration, the three vertical semiconductorfins 121, 122, and 123 comprise three channel segments which areconnected in parallel to collectively form a single, multi-fin verticalFET device in the first device region R1.

Similarly, the second device region R2 comprises at least one verticalFET device which comprises three vertical semiconductor fins 127, 128and 129 commonly connected at one end to the lower source/drain region104-2 and having separate upper source/drain regions 170-2 epitaxiallygrown on opposing ends of vertical semiconductor fins 127, 128 and 128.The vertical source/drain contact 190-2 is commonly connected to each ofthe upper source/drain regions 170-2. In this configuration, the threevertical semiconductor fins 127, 128, and 129 comprise three channelsegments which are connected in parallel to collectively form a single,multi-fin vertical FET device in the second device region R2, therebyeffectively providing separate conductive gate structures in thedifferent device regions R1 and R2.

In the example embodiment of FIG. 1, the lower insulating spacer 130serves to electrically insulate the lower source/drain regions 104-1 and104-2 from the conductive gate structure 155, and the upper insulatingspacer 160 serves to electrically insulate the upper source/drainregions 170-1 and 170-2 from the conductive gate structure 155. Whilethe conductive gate structure 155 is commonly formed through the firstand second device regions R1 and R2 and the isolation region, thevertical dummy fins 124′, 125′, and 126′ are formed of an insulatingmaterial such as silicon nitride or other similar materials, whicheffectively insulates the portion of the conductive gate structure 155in the first device region R1 from the portion of the conductive gatestructure 155 in the second device region R2.

The vertical dummy fins 124′, 125′, and 126′ are formed on the STI layer110 in the isolation region R3 as part of a vertical FET fabricationprocess flow to enable the formation of vertical FET devices in thefirst and second device regions R1 and R2 with uniform structuralprofiles. Indeed, as explained in further detail below, the process flowfor forming the vertical dummy fins 124′, 125′, and 126′ serves tominimize or otherwise eliminate micro-loading effects from a dry etchprocess that is used to pattern the vertical semiconductor fins 121,122, 123, 127, 128 and 129 of the vertical FET devices in the deviceregions R1 and R2. In addition, the process flow for forming thevertical dummy fins 124′, 125′, and 126′ serves to minimize or otherwiseeliminate non-uniform topography and micro-loading effects whenplanarizing and recessing a conductive gate layer to form the conductivegate structure 155, thereby enabling the formation of the conductivegate structure 155 with a uniform gate length (Lg) for the vertical FETdevices across the first and second device regions R1 and R2.

Methods for fabricating the semiconductor device 100 shown in FIG. 1will now be discussed in further detail with reference to FIG. 2 throughFIG. 18, which schematically illustrate the semiconductor device 100 atvarious stages of fabrication. To begin, FIG. 2 is a schematiccross-sectional side view of the semiconductor device 100 at anintermediate stage of fabrication in which a lower source/drain layer104 and a monocrystalline semiconductor layer 106 are formed on thesemiconductor substrate 102. While the semiconductor substrate 102 isgenerically illustrated in FIG. 2, the semiconductor substrate 102 maycomprise one of different types of semiconductor substrate structures.

For example, in one embodiment, the semiconductor substrate 102 maycomprise a bulk semiconductor substrate formed of, e.g., silicon, orother types of semiconductor substrate materials that are commonly usedin bulk semiconductor fabrication processes such as germanium,silicon-germanium alloy, silicon carbide, silicon-germanium carbidealloy, or compound semiconductor materials (e.g. III-V and II-VI).Non-limiting examples of compound semiconductor materials includegallium arsenide, indium arsenide, and indium phosphide. In anotherembodiment, the semiconductor substrate 102 may comprise an activesemiconductor layer (e.g., silicon layer, SiGe layer, III-V compoundsemiconductor layer, etc.) of a SOI (silicon on insulator) substrate,which comprises an insulating layer (e.g., oxide layer) disposed betweena base substrate layer (e.g., silicon substrate) and the activesemiconductor layer 102 in which active circuit components (e.g.,vertical FET devices) are formed as part of a front-end-of-line (FEOL)layer.

The lower source/drain layer 104 and the monocrystalline semiconductorlayer 106 are formed using known techniques and materials. For example,in one embodiment, the lower source/drain layer 104 comprises a dopedepitaxial semiconductor layer that is epitaxially grown on a surface ofthe semiconductor substrate 102, and the monocrystalline semiconductorlayer 106 comprises an epitaxial semiconductor layer that is epitaxiallygrown on a surface of the lower source/drain layer 104. In oneembodiment, the monocrystalline semiconductor layer 106 is undoped. Inanother embodiment, the monocrystalline semiconductor layer 106 islightly doped with doping concentration, for example, of less than5×10¹⁸/cm³. As explained in further detail below, the lower source/drainlayer 104 is subsequently patterned to form the lower source/drainregions 104-1 and 104-2 of the vertical FET devices shown in FIG. 1, andthe undoped monocrystalline semiconductor layer 106 is subsequentlypatterned to form the vertical semiconductor fins 121, 122, 123, 127,128 and 129 of the vertical FET devices shown in FIG. 1.

The type of epitaxial semiconductor material that is used to form thelower source/drain layer 104 will vary depending on various factorsincluding, but not limited to, the type of semiconductor material usedto grow the monocrystalline semiconductor layer 106 (lattice-matchedsemiconductor materials), the device type (e.g., n-type or p-type) ofthe vertical FET devices, etc. For example, for n-type vertical FETdevices, the lower source/drain layer 104 may comprise a doped epitaxialsilicon (Si) material, and for p-type vertical FET devices, the lowersource/drain layer 104 may comprise a doped epitaxial silicon-germanium(SiGe) layer. Moreover, in one embodiment, the undoped monocrystallinesemiconductor layer 106 may comprise an undoped single crystal Si layer.The lower source/drain layer 104 and the monocrystalline semiconductorlayer 106 can be formed with other types of semiconductor materials(e.g., III-V compound semiconductor materials) which are commonly usedto form source/drain regions and vertical semiconductor fins forvertical FET devices.

Furthermore, the lower source/drain layer 104 can be doped using knowntechniques. For example, in one embodiment, the lower source/drain layer104 is in-situ doped wherein dopants are incorporated into the lowersource/drain layer 104 during epitaxial growth of the lower source/drainlayer 104 using a dopant gas such as, for example, a boron-containinggas such as BH₃ for pFETs or a phosphorus or arsenic containing gas suchas PH₃ or AsH₃ for nFETs. In another embodiment, dopants can beincorporated in the lower source/drain layer 104 after the epitaxyprocess using doping techniques such as ion implantation.

In yet another embodiment, the lower source/drain layer 104 can beformed without epitaxy. For example, the lower source/drain layer 104can be formed by adding dopants into a surface of the semiconductorsubstrate 102 (to a target depth which defines a thickness of the lowersource/drain layer 104) using doping techniques such as ionimplantation, gas phase doping, plasma doping, plasma immersion ionimplantation, cluster doping, infusion doping, liquid phase doping,solid phase doping, etc. The monocrystalline semiconductor layer 106 isthen epitaxially grown on the lower source/drain layer 104. The dopingconcentration in the lower source/drain layer 104 can be in a range fromabout 1×10¹⁹/cm³ to about 4×10²¹/cm³. In some embodiments, the lowersource/drain layer 104 may comprise different materials in differentdevice regions, e.g., a first material for n-type vertical FET devices,and another material for p-type vertical FET devices. Similarly, themonocrystalline semiconductor layer 106 may comprise different materialsin different device regions, e.g., a first material for n-type verticalFET devices, and another material for p-type vertical FET devices.

In another embodiment of the invention, the lower source/drain layer 104can be formed by ion implantation of dopants into the surface of thesemiconductor substrate 102 to form a buried doped layer at a targetlevel below the surface of the semiconductor substrate 102. For example,in this embodiment, the various layers 102, 104 and 106 may represent anupper surface of a undoped monocrystalline silicon substrate, whereinthe lower source/drain layer 104 is formed by implanting dopants at asufficient ion implantation energy to form the lower source/drain layer104 at target depth below the surface of the semiconductor substratelayer (wherein a range of target depths define the initial thickness ofthe undoped monocrystalline layer 106). A thermal anneal process can beperformed following the ion implantation process to recrystallizeportions of the semiconductor substrate which may be partially damagedby the ion implantation, as is known in the art.

A next stage of the fabrication process comprises forming a STIstructure in the isolation R3, using a process flow as schematicallyshown in FIGS. 3 and 4. In particular, FIG. 3 is a schematiccross-sectional side view of the semiconductor structure of FIG. 2 afterforming a STI layer 110 which defines and isolates the active deviceregions R1 and R2. In one embodiment of the invention, the STI layer 110is formed by a process which comprises depositing and patterning a padnitride layer (e.g., silicon nitride layer) to form an etch hardmask 108with an opening that defines an image of a shallow trench that is etcheddown through the layers 106 and 104 into the semiconductor substratelayer 102, depositing a layer of insulating material, such as siliconoxide, to fill the shallow trench, and then planarizing the overburdenlayer of insulating material down to the surface of the etch hardmask108, to thereby form the STI layer 110 as shown in FIG. 3. The STI layer110 extends into the substrate 102 below the lower source/drain layer104, thereby patterning the lower source/drain layer 104 to form theseparate lower source/drain regions 104-1 and 104-2 of the vertical FETdevices in the device regions R1 and R2. In one embodiment, the STIlayer 110 is formed by filling the shallow trench with one type ofinsulating material such as silicon oxide. In another embodiment, theSTI layer 110 is formed with multiple insulating materials, e.g.,forming a silicon nitride liner to line the shallow trench, anddepositing a silicon oxide material over the liner to fill the shallowtrench.

Next, FIG. 4 is a schematic cross-sectional side view of thesemiconductor structure of FIG. 3 after recessing the STI layer 110 downto a lower region of the monocrystalline semiconductor layer 106. In oneembodiment, the STI recess is performed using a dry etch process (e.g.,RIE) to etch the STI layer 110 selective to the material of the etchhardmask 108. In one embodiment, the recess process is terminated usinga timed etch process in which a recessed surface 110-1 of the STI layer110 remains above the lower source/drain regions 104-1 and 104-2. TheSTI recess process results in the formation of a trench 110-2 above therecessed STI layer 110 in the isolation region R3.

A next stage of the semiconductor fabrication process comprises fillingthe trench 110-2 with a sacrificial semiconductor material, and thenpatterning the sacrificial semiconductor material concurrently with themonocrystalline semiconductor layer 106 to form an array of verticalsemiconductor fins across the device and isolation regions R1, R2, andR3, using a process flow as schematically illustrated in FIGS. 5, 6, and7. In particular, FIG. 5 is a schematic cross-sectional side view of thesemiconductor structure of FIG. 4 after forming a sacrificialsemiconductor layer 112 on the recessed STI layer 110. In oneembodiment, the sacrificial semiconductor layer 112 is formed bydepositing a layer of semiconductor material to fill the trench 110-2(FIG. 4), performing a planarization process (e.g., CMP) to remove theoverburden semiconductor material down to the surface of the etchhardmask 108, and then performing an etch process to recess thesacrificial semiconductor layer 112 down to a level that issubstantially level with an upper surface of the monocrystallinesemiconductor layer 106, as shown in FIG. 5.

In one embodiment, the sacrificial semiconductor layer 112 is formedwith a semiconductor material which has the same or similar dry etchproperties (e.g., RIE etch properties) as the semiconductor materialthat forms the monocrystalline semiconductor layer 106, but which hasdifferent wet etch properties from the monocrystalline semiconductorlayer 106. In another embodiment, the sacrificial semiconductor layer112 is formed with a semiconductor material which has the same orsimilar dry etch properties (e.g. RIE etch properties) as thesemiconductor material that forms the monocrystalline semiconductorlayer 106 when a first dry etch chemistry is used, but which hasdifferent dry etch properties from the monocrystalline semiconductorlayer 106 when a second dry etch chemistry is used, which is differentfrom the first dry etch chemistry.

For example, when the monocrystalline semiconductor layer 106 is formedof single crystal Si, the sacrificial semiconductor layer 112 can beformed of amorphous Si, amorphous SiGe, polycrystalline Si,polycrystalline SiGe, etc. In addition, when the monocrystallinesemiconductor layer 106 is formed of single crystal SiGe, thesacrificial semiconductor layer 112 can be formed of Si, amorphous SiGe,or polycrystalline SiGe, etc. By way of further example, when themonocrystalline semiconductor layer 106 is formed of a III-V compoundsemiconductor such as gallium arsenide (GaAs), the sacrificialsemiconductor layer 112 can be formed gallium arsenide phosphide (GaAsP)or indium gallium arsenide indium (InGaAs). When the monocrystallinesemiconductor layer 106 is formed of monocrystalline Si, and thesacrificial semiconductor layer 112 is formed of amorphous orpolycrystalline Si or SiGe, the different layers 106 and 112 can havethe same or similar dry etch properties via RIE, while a gas phase etchcontaining HCl (hydrochloride or hydrochloric acid) can be used to etchthe material of the sacrificial semiconductor layer 112 selective to thematerial of the monocrystalline semiconductor layer 106.

Next, FIG. 6 is a schematic cross-sectional side view of thesemiconductor structure of FIG. 5 after forming a hardmask layer 114 onthe surface of the semiconductor structure. In one embodiment, thesemiconductor structure shown in FIG. 6 is formed by stripping away theetch hardmask 108 (FIG. 5), and then depositing a layer of dielectricmaterial, such as silicon nitride (SiN), to cover the upper surfaces ofthe monocrystalline and sacrificial semiconductor layers 106 and 112. Anext step in the illustrative fabrication process comprises patterningthe hardmask layer 114 to form an etch hardmask that is used to etch apattern of vertical fin structures in the device regions R1 and R2 andthe isolation region R3.

For example, FIG. 7 is a schematic cross-sectional side view of thesemiconductor structure of FIG. 6 after patterning the hardmask layer114 to form an etch hardmask 114-1, and patterning the monocrystallinesemiconductor layer 106 and the sacrificial semiconductor layer 112using the image of the etch hardmask 114-1 to form an array of verticalfin structures 120 throughout the regions R1, R2, and R3. Morespecifically, in the illustrative embodiment shown in FIG. 7, the arrayof vertical fin structures 120 comprises vertical semiconductor fins121, 122, and 123 in the first device region R1, sacrificial verticalsemiconductor fins 124, 125, and 126 in the isolation region R3, andvertical semiconductor fins 127, 128, and 129 in the second deviceregion R2. The etch hardmask 114-1 is formed by patterning the hardmasklayer 114 (FIG. 6) using known techniques including, but not limited to,standard photolithography techniques or sidewall image transfer (SIT)techniques, etc. A directional dry etch process (e.g., RIE) is thenperformed using the etch hardmask 114-1 to etch exposed portions of themonocrystalline semiconductor layer 106 down to the lower source/drainregions 104-1 and 104-2, and to etch exposed portions of the sacrificialsemiconductor layer 112 down to the recessed STI layer 110, therebyforming the array of vertical fins 120 over the regions R1, R2, and R3.

In the example embodiment of FIG. 7, the exposed portions of themonocrystalline semiconductor layer 106 in the active device regions R1and R2 and the exposed portions of the sacrificial semiconductor layer112 in the isolation region R3 are anisotropically etched using a dryetch plasma process (e.g., RIE) with an etch chemistry that is suitableto etch the semiconductor materials of the monocrystalline semiconductorlayer 106 and the sacrificial semiconductor layer 112 selective to thematerials of the etch hardmask 114-1, the source/drain regions 104-1,104-2, and the STI layer 110. As noted above, the semiconductormaterials that are used to form the monocrystalline semiconductor layer106 and the sacrificial semiconductor layer 112 have the same orsubstantially the same dry etch properties to eliminate or substantiallyreduce micro-loading effects during the dry etch process.

In particular, since the monocrystalline semiconductor layer 106 and thesacrificial semiconductor layer 112 are formed with semiconductormaterials that have the same or substantially the same dry etchproperties, the concurrent patterning of the sacrificial semiconductorlayer 112 to form the sacrificial vertical semiconductor fins 124, 125,and 126 in the isolation region R3 serves to reduce or eliminate themicro-loading effects that the dry etch process would have on theformation of the vertical semiconductor fins 121, 122, 123, 127, 128 and129 in the active device regions R1 and R2, thus enabling the formationof the vertical semiconductor fins 121, 122, 123, 127, 128 and 129 withuniform structural profiles. For example, if the sacrificial verticalsemiconductor fins 124, 125, and 126 were not concurrently formed in theisolation region R3 during the dry etch process, then the verticalsemiconductor fins 123 and 127 adjacent to the isolation region R3 wouldhave non-uniform structural profiles (e.g., different sidewall profiles)due to the different micro-etch chemistries that would exist in theactive device and isolation regions adjacent to the opposing sidewallsof the semiconductor fins 123 and 127. However, the concurrentpatterning of the array of vertical fins 120 across the device andisolation regions R1, R2, and R3 enables the formation of the verticalsemiconductor fins 121, 122, 123, 127, 128 and 129 with uniformstructural profiles across the active device regions R1 and R2, which isdesired.

As shown in FIG. 7, in one embodiment, the vertical semiconductor fins121, 122, 123, 127, 128 and 129 in the active device regions R1 and R2,and the sacrificial vertical semiconductor fins 124, 125, and 126 in theisolation region R3, are patterned to have the same width (W) and pitch(P) throughout the regions R1, R2, and R3, as well as the same length(not shown) in the Y-direction. In addition, the vertical semiconductorfins 121, 122, 123, 127, 128 and 129 in the active device regions R1 andR2 are formed with a height H, which is defined by the thickness of themonocrystalline semiconductor layer 106. In one example embodiment, thewidth W of the vertical fins 120 is in a range of about 5 nm to about 20nm, the length of the vertical fins 120 is in a range of about 50 nm toabout 1000 nm, and the pitch P of the vertical fins 120 is in a range ofabout 20 nm to about 100 nm. Further, the height H of the verticalsemiconductor fins 121, 122, 123, 127, 128 and 129 in the active deviceregions R1 and R2 is in a range of about 30 nm to about 100 nm. Theformation of the sacrificial vertical semiconductor fins 124, 125, and126 in the isolation region R3 with the same with W and pitch P1 as thevertical semiconductor fins 121, 122, 123, 127, 128 and 129 in theactive device regions R1 and R2 serves to reduce or eliminate themicro-loading effects of the dry etch process.

A next phase of the semiconductor fabrication process comprises formingthe conductive gate structure 155 (e.g., metal gate structure) and thelower and upper insulating spacers 130 and 160 (as shown in FIG. 1),using a process flow as schematically illustrated in FIGS. 8-12. Inparticular, FIG. 8 is a schematic cross-sectional side view of thesemiconductor structure of FIG. 7 after forming the lower insulatingspacer 130 and depositing a conformal layer of gate dielectric material140A. In one embodiment, the lower insulating spacer 130 layer is formedby depositing a layer of low-k dielectric material such as SiO₂, SiN,SiBCN or SiOCN, or some other type of dielectric material that iscommonly used to form insulating spacers for vertical FET devices. Inaddition, the lower insulating spacer 130 may be formed using adirectional deposition process in which the dielectric/insulatingmaterial is directly deposited on lateral surfaces, or by blanketdepositing the dielectric/insulating material followed by planarizingand recessing the dielectric/insulating material, using well-knowndeposition and etching techniques.

Further, in one embodiment, the conformal layer of gate dielectricmaterial is formed by depositing one or more conformal layers of gatedielectric material over the surface of the semiconductor structure. Thegate dielectric material may comprise, e.g., nitride, oxynitride, oroxide or a high-k dielectric material having a dielectric constant ofabout 3.9 or greater. In particular, the conformal layer of gatedielectric material 140A can include silicon oxide, silicon nitride,silicon oxynitride, boron nitride, high-k materials, or any combinationof these materials. Examples of high-k materials include, but are notlimited to, metal oxides such as hafnium oxide, hafnium silicon oxide,hafnium silicon oxynitride, lanthanum oxide, lanthanum aluminum oxide,zirconium oxide, zirconium silicon oxide, zirconium silicon oxynitride,tantalum oxide, titanium oxide, barium strontium titanium oxide, bariumtitanium oxide, strontium titanium oxide, yttrium oxide, aluminum oxide,lead scandium tantalum oxide, and lead zinc niobate. The high-k gatedielectric material may further include dopants such as lanthanum,aluminum. In one embodiment of the invention, the conformal layer ofgate dielectric material is formed with a thickness in a range of about0.5 nm to about 2.5 nm, which will vary depending on the targetapplication. The conformal layer of gate dielectric material 140A isdeposited using known methods such as atomic layer deposition (ALD), forexample, which allows for high conformality of the gate dielectricmaterial.

Next, FIG. 9 is a schematic cross-sectional side view of thesemiconductor structure of FIG. 8 after depositing and planarizing alayer of conductive material 150A which is used to form the gateelectrode layer 150 (FIG. 1). The layer of conductive material 150A isformed by depositing a conductive material including, but not limitedto, doped polycrystalline or amorphous silicon, germanium, silicongermanium, a metal (e.g., tungsten, titanium, tantalum, ruthenium,zirconium, cobalt, copper, aluminum, lead, platinum, tin, silver, gold),a conducting metallic compound material (e.g., tantalum nitride,titanium nitride, tantalum carbide, titanium carbide, titanium aluminumcarbide, tungsten silicide, tungsten nitride, ruthenium oxide, cobaltsilicide, nickel silicide), carbon nanotube, conductive carbon,graphene, or any suitable combination of such conductive materials. Thelayer of conductive material 150A may further comprise dopants that areincorporated during or after deposition. The layer of conductivematerial 150A is deposited using a suitable deposition process, forexample, CVD, PECVD, PVD, plating, thermal or e-beam evaporation,sputtering, etc.

In another embodiment, a thin conformal layer of work function metal(WFM) may be deposited over the conformal layer of gate dielectricmaterial 140A prior to depositing the layer of conductive material 150A.The thin conformal WFM layer can be formed of one or more types ofmetallic materials, including, but not limited to, TiN, TaN, TiAlC, Zr,W, Hf, Ti, Al, Ru, Pa, TiAl, ZrAl, WAl, TaAl, HfAl, TiAlC, TaC, TiC,TaMgC, or other work function metals or alloys that are commonly used toobtain target work functions which are suitable for the type (e.g.,n-type or p-type) of vertical FET devices that are to be formed. Theconformal WFM layer is deposited using known methods such as ALD, CVD,etc. In one embodiment, the conformal WFM layer is formed with athickness in a range of about 2 nm to about 5 nm. In another embodiment,the conductive material 150A that forms the gate electrode layer 150 canserve as a WFM layer.

Following the deposition of the layer of conductive material 150A, aplanarization process (e.g., CMP) is performed to polish the surface ofthe semiconductor structure down to the conformal layer of gatedielectric material 140A, thereby removing the overburden portion of thelayer of conductive material 150A, resulting in the semiconductorstructure shown in FIG. 9. Following the planarizing process, the layerof conductive material 150A is recessed down to form the gate electrodelayer 150. In particular, FIG. 10 is a schematic cross-sectional sideview of the semiconductor structure of FIG. 9 after recessing the layerof conductive material 150A to form the gate electrode layer 150 with arecessed thickness that defines the gate length (Lg) of the vertical FETdevices to be formed in the active device regions R1 and R2. The gaterecess can be performed using well known etch-back/recess techniques inwhich a timed etch process is performed to etch the layer of conductivematerial 150A down to a target recess level to form the gate electrodelayer 150.

During the CMP process, the presence of the sacrificial verticalsemiconductor fins 124, 125, and 126 in the isolation region R3 servesto prevent over polishing of the layer of conductive material 150A(e.g., CPM dishing/erosion) in the isolation region R3, which wouldtypically occur in the isolation region R3 as a result of the CMPprocess without the presence of the sacrificial vertical semiconductorfins 124, 125, and 126. By preventing CMP dishing/erosion of layer ofconductive material 150A in the isolation region R3, a more uniformrecess is achieved when recessing the layer of conductive material 150Adown to the target level (via the timed etch process) to define the gatelength Lg.

For example, without the sacrificial vertical semiconductor fins 124,125, and 126 in the isolation region R3, the initial thickness of theconductive material 150A on the sidewalls of the vertical semiconductorfins 123 and 127 adjacent the isolation region R3 may be less than thethickness of the conductive material 150A on the opposing sidewalls ofthe vertical semiconductor fins 123 and 127 adjacent to the deviceregions R1 and R2. As a result of this initial non-uniform thickness,the gate recess process would result in non-uniform gate lengths Lg ofthe resulting gate electrode layer 150 on the opposing sides of thevertical semiconductor fins 123 and 127. In short, the presence of thesacrificial vertical semiconductor fins 124, 125, and 126 in theisolation region R3 ensures that all vertical semiconductor fins in theactive device regions R1 and R2 have the same patterning environment,thus resulting in a uniform gate recess (i.e., uniform Lg) in the activedevice regions R1 and R2.

Next, FIG. 11 is a schematic cross-sectional side view of thesemiconductor structure of FIG. 10 after removing exposed portions ofthe gate dielectric layer 140A on upper portions of the vertical fins121˜129 in the active device and isolation regions R1, R2, and R3,thereby forming the conductive gate structure 155 for the vertical FETdevices in the active device regions R1 and R2. The exposed portions ofthe gate dielectric layer 140A are etched using a dry or wet etchprocess which is selective to the materials of the vertical fins 120,the gate electrode layer 150, and the etch hardmask 114-1. As notedabove, the portions of the conductive gate structure 155 in the firstand second active device regions R1 and R2 are electrically isolated bythe insulting dummy fin structures 124′, 125′, and 126′ that aresubsequently formed to replace the sacrificial vertical semiconductorfins 1124, 125, and 126 in the isolation region R3. In anotherembodiment, the exposed portions of the gate dielectric layer 140A onthe upper portion of the vertical fins 120 are not removed (i.e.,etching away the exposed portions of the gate dielectric 140A isoptional).

Next, FIG. 12 is a schematic cross-sectional side view of thesemiconductor structure of FIG. 11 after forming the upper insulatingspacer 160 on the upper surface of the conductive gate structure 155. Inone embodiment, the upper insulating spacer 160 is formed of the same orsimilar low-k dielectric materials and using the same or similardeposition techniques as discussed above with regard to the lowerinsulating spacer 130. Other suitable techniques can also be used toform the upper insulating spacer 160.

A next phase of the semiconductor fabrication process comprisesreplacing the sacrificial vertical semiconductor fins 124, 125, and 126with insulating material to form the vertical dummy fin structures 124′,125′ and 126′ in the isolation region R3, using a process flow asschematically illustrated in FIGS. 13˜17. In particular, FIG. 13 is aschematic cross-sectional side view of the semiconductor structure ofFIG. 12 after depositing a layer of insulating material 165 (e.g.,silicon oxide) on the surface of the semiconductor structure andremoving the overburden insulating material by planarizing (e.g., CMP)the surface of the semiconductor structure down to the etch hardmask114-1 on top of the vertical fins 120 in the active device and isolationregions R1, R2, and R3. The layer of insulating material 165 is formedof a material that has etch selectivity relative to the material of theetch hardmask 114-1, which enables selective removal of the etchhardmask 114-1 as shown in FIG. 14.

In particular, FIG. 14 is a schematic cross-sectional side view of thesemiconductor structure of FIG. 13 after removing the etch hardmask114-1 to form shallow trenches 114-2 which expose the upper surfaces ofthe vertical fins 120 in the active device and isolation regions R1, R2,and R3. The etch hardmask 114-1 can be removed using a dry or wet etchprocess having an etch chemistry that is configured to etch away thematerial of the etch hardmask 114-1 selective to the materials of theinsulating layer 165 and the vertical fins 120.

Next, FIG. 15 is a schematic cross-sectional side view of thesemiconductor structure of FIG. 14 after removing the sacrificialvertical semiconductor fins 124, 125, and 126 in the isolation region R3to form trenches 124-1, 125-1, and 126-1, respectively, down to the STIlayer 110. In one embodiment of the invention, the sacrificial verticalsemiconductor fins 124, 125, and 126 are removed using a wet etchprocess (or other suitable etch process) that is selective to thesemiconductor material which forms the vertical semiconductor fins 121,122, 123, 127, 128 and 129 in the active device regions R1 and R2. Inthis manner, the sacrificial vertical semiconductor fins 124, 125, and126 in the isolation region R3 can be removed without etching ordamaging the vertical semiconductor fins 121, 122, 123, 127, 128 and 129in the active device regions R1 and R2.

For example, in one embodiment of the invention, a wet solutioncontaining ammonia (NH₄OH) and hydrogen peroxide (H₂O₂) can be used toetch away the sacrificial vertical semiconductor fins 124, 125, and 126in the isolation region R3 selective to the vertical semiconductor fins121, 122, 123, 127, 128 and 129 in the active device regions R1 and R2.In another embodiment, as noted above, a gas phase HCl (hydrochloricacid) can be used to etch away the sacrificial vertical semiconductorfins 124, 125, and 126 in the isolation region R3 highly selective tothe vertical semiconductor fins 121, 122, 123, 127, 128 and 129 in theactive device regions R1 and R2 when, for example, the verticalsemiconductor fins 121, 122, 123, 127, 128, and 129 are formed ofmonocrystalline Si, and the sacrificial vertical semiconductor fins 124,125, and 126 are formed of amorphous SiGe or polycrystalline SiGe.

A next step in the fabrication process is shown in FIG. 16, which is aschematic cross-sectional side view of the semiconductor structure ofFIG. 15 after filling the trenches 114-2, 124-1, 125-1, and 126-1 withan insulating material 168 to form the vertical dummy fins 124′, 125′,and 126′ in the isolation region R3. In one embodiment of the invention,the vertical dummy fins 124′, 125′, and 126′ are formed by depositing alayer of insulating material, such as silicon nitride, silicon oxide,SiBCN, SiCO, SiOCN, or any suitable combination of those materials, tofill the trenches, and then planarizing the surface of the semiconductorstructure to remove the overburden insulating material down to theinsulating layer 165, resulting in the semiconductor structure shown inFIG. 16. By forming the vertical dummy fins 124′, 125′, and 126′ with aninsulating material, the portions of the conductive gate structure 155in the adjacent active device regions R1 and R2 are effectivelyelectrically isolated/insulated from each other.

Next, FIG. 17 is a schematic cross-sectional side view of thesemiconductor structure of FIG. 16 after performing an etch process torecess the insulating material 168 down to a level which exposes theupper surfaces of the vertical semiconductor fins 121, 122, 123, 127,128, and 129 in the active device regions R1 and R2. This etch processalso results in recessing the upper surfaces of the vertical dummy fins124′, 125′, and 126′ in the isolation region R3 to be substantiallylevel with the upper surfaces of the vertical semiconductor fins 121,123, 123, 127, 128, and 129 in the active device regions R1 and R2, asshown in FIG. 17.

Following the recess process, the layer of insulating material 165 isremoved to expose upper portions of the vertical semiconductor fins 121,123, 123, 127, 128, and 129 on which the upper source/drain regions areepitaxially grown. For example, FIG. 18 is a schematic cross-sectionalside view of the semiconductor structure of FIG. 17 after removing thelayer of insulating material 165 on the surface of the upper insulatingspacer 160, and epitaxially growing the upper source/drain regions 170-1and 170-2 on the exposed upper portions of the vertical semiconductorfins 121, 122, 123, 127, 128, and 129 in the respective active deviceregions R1 and R2.

In one embodiment, the upper source/drain regions 170-1 and 170-2 areformed by epitaxially growing doped semiconductor layers (e.g., dopedSiGe) on the exposed upper portions of the vertical semiconductor fins121, 122, 123, 127, 128, and 129 using known selective growth techniquesin which the epitaxial material is not grown on the exposed surfaces ofupper insulating spacer 160 or on the exposed upper portions of thevertical dummy fins 124′, 125′ and 126′. The type of epitaxialsemiconductor material that is used to form the upper source/drainregions 170-1 and 170-2 will vary depending on various factorsincluding, but are not limited to, the type of material of the verticalsemiconductor fins 121, 122, 123, 127, 128, and 129, the device type(e.g., n-type or p-type) of the vertical FET devices to be formed in theactive device regions R1 and R2, etc.

As shown in the example embodiment of FIG. 18, the upper source/drainregions 170-1 and 170-2 comprise diamond-shaped (or faceted)source/drain structures, which can be formed using known techniques inwhich the process conditions are adjusted to vary the growth rate onsurfaces with different crystallographic orientations, as is known inthe art. The epitaxial growth may continue until merger of the epitaxialgrown layers on the upper surfaces of adjacent vertical semiconductorfin structures. In some embodiments, the faceted source/drain regions170-1 and 170-2 may be in-situ doped during epitaxial growth by adding adopant gas to the source deposition gas (i.e., the Si-containing gas).Exemplary dopant gases may include a boron-containing gas such as BH₃for pFETs or a phosphorus or arsenic containing gas such as PH₃ or AsH₃for nFETs, wherein the concentration of impurity in the gas phasedetermines its concentration in the deposited film. Alternatively, theupper source/drain regions 170-1 and 170-2 can be doped ex-situ using,for example, ion implantation, gas phase doping, plasma doping, plasmaimmersion ion implantation, cluster doping, infusion doping, liquidphase doping, solid phase doping, etc. In one non-limiting embodiment,the doping concentration can range from about 1×10¹⁹/cm³ to about4×10²¹/cm³. While the example embodiment of FIG. 18 shows diamond-shapedepitaxial structures, the upper source/drain regions 170-1 and 170-2 canbe formed to have other types of shapes.

Following the formation of the semiconductor structure shown in FIG. 18,any known sequence of processing steps can be implemented to completethe fabrication the semiconductor integrated circuit device as shown inFIG. 1, the details of which are not needed to understand embodiments ofthe invention. Briefly, by way of example, referring back to FIG. 1,after forming the upper source/drain regions 170-1 and 170-2, a FEOLprocess and MOL (middle of the line) process are continued to form theinsulating layer 180, pattern the insulating layer 180 to form trenchesand/or via openings to expose the upper source/drain regions 170-1 and170-2, and then fill the trenches and/or via openings with conductivematerial to form the vertical source/drain contacts 180-1 and 180-2. Inaddition, vertical contacts (not shown) to the lower source/drainregions 104-1 and 104-2 and the different portions of the conductivegate structure 155 in the active device regions R1 and R2 are fabricatedusing known methods. Following formation of the vertical devicecontacts, a BEOL (back end of line) interconnect structure is formed toprovide connections to/between the vertical FET devices and other activeor passive devices that are formed as part of the FEOL layer in theactive device regions R1 and R2.

It is to be understood that the methods discussed herein for fabricatingvertical FET devices with uniform structural profiles can beincorporated within semiconductor processing flows for fabricating othertypes of semiconductor devices and integrated circuits with variousanalog and digital circuitry or mixed-signal circuitry. In particular,integrated circuit dies can be fabricated with various devices such asfield-effect transistors, bipolar transistors, metal-oxide-semiconductortransistors, diodes, capacitors, inductors, etc. An integrated circuitin accordance with the present invention can be employed inapplications, hardware, and/or electronic systems. Suitable hardware andsystems for implementing the invention may include, but are not limitedto, personal computers, communication networks, electronic commercesystems, portable communications devices (e.g., cell phones),solid-state media storage devices, functional circuitry, etc. Systemsand hardware incorporating such integrated circuits are considered partof the embodiments described herein. Given the teachings of theinvention provided herein, one of ordinary skill in the art will be ableto contemplate other implementations and applications of the techniquesof the invention.

Although exemplary embodiments have been described herein with referenceto the accompanying figures, it is to be understood that the inventionis not limited to those precise embodiments, and that various otherchanges and modifications may be made therein by one skilled in the artwithout departing from the scope of the appended claims.

What is claimed is:
 1. A method for fabricating a semiconductor device,comprising: forming a substrate comprising a lower source/drain layerdisposed between a base semiconductor substrate and a first layer ofsemiconductor material; forming a shallow trench isolation (STI) layerthrough a portion of the first layer of semiconductor material, thelower source/drain layer and into an upper portion of the semiconductorsubstrate to form an isolation region, wherein the isolation regiondefines a first device region comprising a first lower source/drainregion and a second device region comprising a second lower source/drainregion; recessing the STI layer; forming a second layer of semiconductormaterial on the recessed STI layer in the isolation region; concurrentlypatterning the first and second layers of semiconductor material using afirst etch process to form an array of vertical semiconductor tins inthe first and second device regions and the isolation region; forming alower insulating spacer on the first and second lower source/drainregions and the STI layer; forming a conductive gate structure on thelower insulating spacer and surrounding sidewalls of the verticalsemiconductor fins in the first and second device regions and theisolation region; forming an upper insulating spacer on the conductivegate structure; etching away the vertical semiconductor fins in theisolation region using a second etch process which is selective to thevertical semiconductor fins in the first and second device regions, toform trenches down to the STI layer in the isolation, region; andfilling the trenches in the isolation region with insulating material toform vertical dummy fins in the isolation region.
 2. The method of claim1, further comprising epitaxially growing upper source/drain regions onexposed upper portions of the vertical semiconductor tins in the firstand second device regions.
 3. The method of claim 1, wherein the firstlayer of semiconductor material comprises a layer of monocrystallinesemiconductor material, and wherein the second layer of semiconductormaterial comprises a layer of amorphous or polycrystalline semiconductormaterial.
 4. The method of claim 1, wherein the first layer ofsemiconductor material comprises monocrystalline silicon and wherein thesecond layer of semiconductor material comprises amorphous silicongermanium or polycrystalline silicon germanium.
 5. The method of claim1, wherein the first etch process comprises a dry etch process having anetch chemistry that is non-selective to the first and second layers ofsemiconductor material, and wherein the second etch process comprises adry or wet etch process having an etch chemistry that is selective tothe first layer of semiconductor material.
 6. The method of claim 1,wherein the vertical semiconductor fins in the first and second deviceregions and the vertical dummy tins in the isolation region havesubstantially a same width and are spaced by substantially a same pitch.7. The method of claim 1, wherein filling the trenches in the isolationregion with insulating material to form the vertical dummy fins in theisolation region comprises filling the trenches with a nitride material.8. The method of claim 1, wherein forming the conductive gate structureon the lower insulating spacer and surrounding the sidewalls of thevertical semiconductor fins in the first and second device regions andthe isolation region, comprises: forming a conformal layer of gatedielectric material to cover the vertical semiconductor fins and thelower insulating spacer in the first and second device regions and theisolation region; depositing a layer of conductive material to fillspaces between the vertical semiconductor fins in the first and seconddevice regions and the isolation region with conductive material; andrecessing the layer of conductive material down to a target level belowan upper surface of the vertical semiconductor fins in the first andsecond device regions and the isolation region, wherein the target leveldefines a gate length of the conductive gate structure of the verticalsemiconductor fins in the first and second device regions.
 9. The methodof claim 1, wherein forming the substrate comprises epitaxially growingthe lower source/drain layer on a surface of the base semiconductorsubstrate; and epitaxially growing the first layer of semiconductormaterial on the lower source/drain layer.